March 2013     21 2. Cracks found on the surface of the LNG plant (red) and internal cracks on the cut sections.     2. Surface cracks on the ING plant and internal SCC cracks on the cut section. 2. Liquefied Natural Gas (‘LNG’) plant Cracking was detected in a stainless steel process vessel in a Middle Eastern LNG Plant. The cracking was restricted to a narrow band of the vessel and only affected the outside, non-processing side of the vessel. Dye Penetrant Inspection revealed that the cracking was extensive, and occurred preferentially near welded joints. Examination of cut samples showed fine branching cracks typical of stress corrosion cracking and chemical analysis showed the presence of chlorides within the cracks (pictured above). The vessel operated in a dry desert environment, so it had to be discovered how the chlorides had causes SCC. The upper parts of the column operated at -100°C and ice was present on the outer surface of the vessel. As the temperature reduced further down the column the ice melted to form water in the region where SCC had occurred. The vessel was located on the coast and this water was able to absorb salt from the environment. Over the 9 years of operation this solution concentrated until SCC occurred (pictured above). 3. Pilot vessel A British pilot vessel was found to be suffering from widespread corrosion inside the aluminium hull. Examination of samples indicated that this was caused by pitting corrosion, although aluminium is not known to pit in sea water (pictured below). Samples of the bilge water were analysed and were found to contain levels of chloride that were significantly higher than those found in sea water but no elevated levels of other marine elements were noted. Chemical residues were then analysed and it was determined that the pitting was caused by residues of cleaning products.     3. The pilot vessel and pitting corrosion found on the internal surface of the hull © 2013 Xchanging